1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a video camera and a digital still camera, and more particularly to an image pickup apparatus that serves to perform digital zooming along with optical zooming.
2. Description of the Related Art
Some image pickup apparatuses, such as a video camera, have an optical zoom function that varies a magnification by moving a magnification-varying lens in an optical system, and an electronic (or digital) zoom function that provides electronic zooming by using an image generated through a photoelectric conversion of a subject image formed by the optical system. An extremely high zoom magnification can be obtained by using the optical zoom function and the electronic zoom function in combination (see Japanese Laid-Open Patent No. 2002-314868).
However, when the electronic zoom magnification is stepwise changed along with a change of the optical zoom magnification in a rear focus mechanism, a moving amount of a focus lens relative to a zoom lens becomes larger at the telephoto side than at the wide-angle end. Therefore, an image magnification variation ratio (change rate) of the optical system is made smaller at a position closer to the telephoto end by mitigating the moving load of the focus lens. On the other hand, when the image magnification variation by the image magnification variation part which is a change of a magnification by the electronic zooming is discrete, it hardly matches the image magnification variation ratio of the above optical system. Then, as zoom moves from the wide-angle end side to the telephoto end side, a zoom speed or a change rate of a synthesis magnification between the optical zoom magnification and the electronic zoom magnification becomes greatly different between the vicinity of the telephoto end and the vicinity of the wide-angle end. Thereby, a user's comfortable zoom manipulation may be impaired.